Multi-spindle machines are known in the prior art. Multi-spindle machines are used to mass produce standardized types of components. A multi-spindle machine typically has several workstations at which machining operations are performed. A piece of raw stock, such as bar stock, enters the machine at a first station and as the machine indexes, various machining operations are performed. Once this station is indexed completely through the machine, a completed part is formed. The part is released, and the process is repeated for that station with a new piece of raw stock. An advantage of multi-spindle machines is that all stations in the machine are producing parts simultaneously, resulting in high production.
Multi-spindle machines typically have a large indexing drum with four, six or eight stations thereon, Each of the stations carries a workpiece. In all but one of the stations, where a new piece of stock enters, a machining operation is performed. After each operation is completed, the drum is rotated so that each workpiece moves sequentially through the location where the various operations are performed. Machining operations typically performed at a multi-spindle machine include turning and threading.
Most multi-spindle machines are very efficient in terms of producing standardized parts at a high rate. They also have drawbacks. A primary drawback associated with multispindle machines is that the entire machine often operates off of a single main motor. The main motor simultaneously drives all of the devices in the machine. Multi-spindle machines typically include a timing shaft for the coordination of multiple machine operations. The operator of the machine is still required to set up the cams operating off the timing shaft which is a very time consuming activity.
The speed of multi-spindle machines typically changes from high to low speed and back again during the course of their operating cycle. High speed is typically used for times in the machine cycle when critical machining operations are not occurring. High speed operation is desirable when the stations are indexing or when the tools are moving toward or away from the work pieces and are not performing work thereon. Low speed operation is used when the tools in the machine are forming the metal. Any attempt to operate the machine at high speed when such forming work is being performed is likely to cause a problem or jam up the machine.
It is the responsibility of the operator or set-up technician to properly set the points in the machine cycle where the machine makes its high speed and low speed shifts. Shifting from high to low speed too early may result in slower cycle times and production rates. The same results may occur if the shift from low to high speed is made too late in the machine cycle. However as previously discussed, if the shift from high to low speed is made too late (or the shift from low to high too early) damage to the machine, the tooling or the workpiece may result.
Another disadvantage of past machine systems is the time lag in the cycle when the machine shifts from high speed to low speed. This time lag is due to the momentum of the gears traveling at the high speed. FIG. 1 shows a cross sectional view of a power feed train and gear layout for a National Acme 7/16 RA6 multi-spindle machine. Referring now to FIG. 1 for illustration of this time lag, there is shown a power feed train and gear layout generally indicated 10. The power feed train consists of a main motor and main motor sprocket (not shown) which engages and drives a main motor pulley 12. The main motor pulley 12 engages a sprocket on a pulley shaft 14. This pulley shaft acts to drive the entire gear train of the multi-spindle machine.
The pulley shaft 14 drives both a high speed drive train and a low speed drive train. Both the high speed and low speed drive trains selectively act to drive the main drum shaft 16 of the machine. The main drum shaft is part of a power drive tin which drives the part forming components of the machine. The low speed drive train consists of a plurality of reducing gear couples which act to substantially reduce rotational speed from that of the pulley shaft 14. The pulley shaft 14 first engages a spindle speed drive gear 20. Spindle speed drive gear 20 propels a meshing spindle speed change gear 22. The spindle speed change gear 22 drives a spindle change gear shaft 24 which also engages a range drive gear 26. The range drive gear meshes with and propels a range gear 28. The range gear 28 drives a second range drive gear 30. The second range drive gear is driven by range gear 28 through a spindle drive shaft 32. Second range drive gear 30 is coupled to a second range gear 34 which drives a feed change gear shaft 36. Feed change gear shaft 36 drives the last speed reducing couple which consists of feed change drive gear 38 and feed change gear 40. The feed change gear 40 drives a small worm shaft 18. The small worm shaft drives a small worm gear 42 which drives a constant speed shaft 50 through a gear 43. The shaft 50 drives the main drum shaft 16 at the low speed, through a large worm drive gear 48 and large worm shaft 54.
The pulley shaft 14 may also selectively transmit power to the main drum 16 shaft through the high speed drive train. The high speed drive train includes drive gear 44 which engages high speed bevel gear 46. The high speed bevel gear 46 drives large worm shaft drive gear 48 through shaft 50. The large worm shaft drive gear 48 is coupled with large worm shaft driven gear 52. Gear 52 drives large worm shaft 54 which drives the main drum shaft worm gear 56. Worm gear 56 turns the main drum shaft 16.
As discussed above, either the low speed drive train or the high speed drive train propels the power drive train at any one time. This is accomplished by having the low speed drive train always operating while the high speed drive train is selectively engaged. When the low speed drive train is selected to drive the main drum shaft, the high speed drive gear 44 is operatively disengaged from the pulley shaft by a high-low speed disc clutch 58. When the high-low speed disc clutch is disengaged, the high speed drive gear 44 is free to rotate independent of the pulley shaft 14. As the low speed drive train drives the small worm gear 42, the constant speed shaft 50 turns the large worm shaft drive gear 48. The rotational speed of the small worm gear 42 determines the speed of the main drum shaft 16.
When the main drum shaft is desired to be rotated at a high speed, the high-low speed disc clutch 58 is engaged allowing the pulley shaft 14 to drive the high speed drive gear 44. The large worm shaft drive gear 48 is then driven by high speed bevel gear 46 through the constant speed shaft 50, to drive the power drive train. During the high speed rotation a roll clutch 60 enables overrunning by shaft 50 of gear 43. The roll clutch 60 allows the constant speed shaft 50 to rotate at a higher speed than the speed imparted to gear 43 rotating small worm gear 42. The roll clutch is a conventional overrunning clutch and permits freewheeling of the constant speed shaft in excess of the speed imparted to gear 43 relative the small worm gear 42.
Large worm shaft 54 in the power drive train can be operatively disconnected from the large worm shaft driven gear 52 by feed disc clutch 62. Feed disc clutch 62 allows for the freewheeling of the large worm shaft 54 when the clutch 62 is disengaged. One situation in which the large worm shaft is disconnected from the large worm shaft driven gear is when the large worm shaft is stopped by a brake 64. The brake 64 conventionally acts to stop the main drum shaft 16 in cases of emergency. In the prior art the brake 64 consists of a typical band brake.
The problem of increased cycle times that result from untimely shifting from high to low speed is inherent in the operation of the power feed train and gear layout 10. As discussed above, in high speed operation the high-low speed disc clutch 58 is engaged with the pulley shaft 14. Shaft 14 drives the constant speed shaft 50 and the large worm shaft drive gear 48 from the relatively high speed of the pulley shaft 14. During high speed rotation of the constant speed shaft 50, the roll clutch 60 operatively disengages the constant speed shaft from the small worm gear 42 by overrunning. During high speed operation gears 42 and 43 rotate at the lower relative speed of the low speed drive train.
When it is desired to shift back into low speed the roll clutch 60 must be operatively re-engaged to allow the small worm gear 42 to transfer power to the large worm shaft drive gear 48. At the same time the low speed disc clutch 58 is disengaged to allow shaft 50 to slow down until the low speed drive train takes over. In this prior art power feed train and gear layout 10, a time lag is necessary to allow tie drum shaft 16 and all of the connected components to slow down before moving in powered condition at the lower speed. When the low speed drive train is engaged the inertia of the normally driven gears tends to overcome the lash of the normally driving gears. This pull increases wear on the gears leading to reduced life.
Undesirably long machine cycle times also result because the forming of parts cannot occur until the machine is being driven at low speed. As a result, the high-low speed clutch 58 must disengage early enough in the cycle to allow the inertia to dissipate before metal working operations begin.
Thus, there exists a need for a control system for a multi-spindle machine that decreases the cycle time, minimizes wear on the drive train gears and enables the more effective operation of a multi-spindle machine.